The present invention relates to an improved process for producing carbonyl sulfide which is useful as the intermediate for agriculture chemicals, medicines and other chemical compounds.
More particularly, it relates to a process for selectively producing carbonyl sulfide having high purity in high efficiency by reacting carbon monoxide with sulfur in the presence of a special catalyst at relatively low temperature under preventing the formation of by-product of carbon disulfide and decreasing the formation of carbon dioxide.
As the process for producing carbonyl sulfide by reacting carbon monoxide with sulfur, it has been proposed to react carbon monoxide with sulfur at relatively high temperature of 350.degree. to 510.degree. C (West German Pat. No. 1,222,024) and to react carbon monoxide with sulfur at relatively low temperature of 260.degree. to 483.degree. C (500.degree. to 900.degree. F) in the presence of an aluminosilicate having a three dimensional structure (U.S. Pat. No. 2,983,580) and to react carbon monoxide with sulfur in the presence of a sulfide having a metal selected from the group consisting of metals in the V, VI, VII and VIII groups of the periodic table (U.S. Pat. No. 3,416,893 and British Pat. No. 957,102) and to react carbon monoxide with sulfur in the presence of an alkali metal sulfide such as sodium and potassiun sulfides (Japanese Patent Publication No. 27632/1972 and U.S. Pat. No. 3,764,661).
However, the inventors have studied and have found that the reaction velocity in the reaction of carbon monoxide with sulfur at 350.degree. to 510.degree. C is remarkably low whereby it is necessary to give remarkably long reaction time for producing carbonyl sulfide in high yield at the temperature.
However, when the reaction time is long, it is difficult to prevent the formation of the by-products of carbon disulfide and carbon dioxide. On the other hand, when the reaction temperature is high for imparting high reaction velocity, the reverse reaction to decompose carbonyl sulfide is caused to decrease the content of the resulting carbonyl sulfide and to increase the contents of carbon monoxide and sulfur, and the metal corrosive action of carbonyl sulfinyl at high temperature is increased to corrode the substrate of the reactor disadvantageously.
In the process for reacting carbon monoxide with sulfur in the presence of aluminosilicate, the selectivity given by the aluminosilicate used as the catalyst is not satisfactory whereby the by-products of carbon disulfide and carbon dioxide can not be prevented.
In the process for reacting carbon monoxide with sulfur in the presence of a metal sulfide having a metal selected from the group consisting of the V, VI VII and VIII groups of the periodic table, all of the metal sulfides used as the catalyst has low selectivity whereby it has been difficult to prevent the formation of the by-products of carbon disulfide and carbon dioxide, and it has been difficult to impart high catalytic activity.
Accordingly, in order to produce carbonyl sulfide under minimizing the formation of the by-products of carbon disulfide and carbon dioxide, it is necessary to react carbon monoxide with sulfur in relatively low conversion that is low reaction efficiency though the catalytic activity is not enough high.
However, when the conversion is low, carbon monoxide of the unreacted material contained in the reaction mixture gas at high ratio should be separated and recovered from carbonyl sulfide. Accordingly, the process is not satisfactory for the industrial operation.
On the other hand, in the process for reacting carbon monoxide with sulfur in the presence of the alkali metal sulfide such as sodium or potassium sulfide, the catalytic activity of the alkali metal sulfide is remarkably high, whereby the catalysts are suitable for increasing the reaction velocity for the reaction of carbon monoxide with sulfur. However, as the result, the selectivity is low and it is difficult to prevent the formation of the by-products of carbon disulfide and carbon dioxide.
The object compound of carbonyl sulfide is the useful intermediate for the source of thiolcarbonyl group --CO--S-- and carbonyl group &gt;C = O, and is especially important as the intermediate for the thiolcarbamic acid derivatives and urea derivatives.
The reaction of carbonyl sulfide is similar to that of carbon disulfide. For example, carbonyl sulfide reacts with secondary amines in the presence of an alkali metal hydroxide to produce thiolcarbamic acid salts. (Reaction formula I). On the other hand, carbon disulfide also reacts with secondary amines to produce dithiocarbamic acid salts (Reaction formula II). ##STR1##
Carbonyl sulfide reacts with primary amines to produce urea. (Reaction formula III). On the other hand, carbon disulfide also reacts with primary amines to produce thiourea. (Reaction formula IV). ##STR2##
On the other hand, carbon dioxide is not cause trouble as carbon disulfide. For example, carbon dioxide reacts with a metal hydroxide to produce carbonate. In order to produce urea severe reaction condition at high temperature under high pressure is required.
The separation of carbon dioxide from carbonyl sulfide is relatively easy in comparison with the separation of carbon disulfide from carbonyl sulfide.
Accordingly, when the urea derivatives and the thiolcarbamic acid derivatives are produced by using carbonyl sulfide containing the by-product of carbon disulfide, the reactions similar to the reaction formula (I) to (IV) are caused to decrease the purity of the products, disadvantageously.
However, it has not been possible to selectively produce carbonyl sulfide under completely preventing the formation of the by-product of carbon disulfide by the conventional processes.